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OE Scheduled Maintenace - Fluids

Recommended fluid service intervals have gradually lengthened over the years. That's an automotive fact of life, and today there are actually quite a few cases of "filled-for-life" systems.

But filled-for-life recommendations also carry some fine print, and ATF is a perfect example. Unless a vehicle is used in the rather gentle conditions called "normal service," the lifetime recommendation for ATF goes down to 50,000 miles. There even are two automatics without dipsticks-the 4T40-E and 4T45-E in the Cavalier/Sunfire. But even these GM transmissions carry a 50,000-mile severe service interval.

Just because some manufacturers are aggressively promoting extended ATF change intervals doesn't mean that everyone is, or even that it's a great idea. A typical ATF replacement interval is 30 months or about 37,500 miles in "normal" service, once a year or 12,000 miles for so-called "severe" operation (short trips, heavy loads, warm temperatures, etc.). In fact, about the only vehicles that can meet the "normal" operation definition would be commuter cars with trips of at least 20 miles or more each way and no traffic-and there are not many of those. Minivans and SUVs used by soccer moms are classic examples of vehicles driven in severe service.

Also remember that the latest service intervals do not apply to the older vehicles you service. Pickup trucks are the most noteworthy example: They're typically kept in service for a long, long time. The specified ATF change interval on GM trucks through the 1980s was 15,000 miles in normal driving, just 12,000 in severe service.

In addition, it's good practice to shorten all fluid service intervals as a vehicle ages. ATF runs hotter than most other fluids, and as it deteriorates it can add to the buildup of deposits that cause hydraulic valves to stick. There may not be much of a buildup at low mileage, but at higher mileage it's important to keep the fluid fresh, because any additional varnish deposits to what's already there can produce shifting complaints.

Manual Transmission Gear Oil

Don't forget to drain and fill manual transmissions. Gear oil may not work as hard as automatic transmission fluid, but if it gets gritty it won't keep shift forks and synchronizers sliding smoothly along the shafts.

Front & Rear Axle Fluid

In some cases, these fluids are specified as "lifetime" with periodic level checks and top-ups. However, it's good practice to drain or siphon out the old stuff and install a fresh fill. A typical truck maintenance spec is approximately every four years or 45,000 to 50,000 miles for a conventional rear axle, six years or 60,000 to 70,000 miles for the front axle on 4WDs. However, it's often shorter on SUVs-such as 2 years/30,000 miles (Jeep Grand Cherokee and even the 2001 Acura MDX), because the axles often are more complex assemblies and the vehicles themselves use 4WD more often.

Many SUV axles have limited-slip clutch packs and even electromagnetic clutches. Use an OE fluid or a replacement recommended for them by a reputable oil company. Remember, the wrong oil can produce chatter and erratic operation.

Transfer Case or Coupling Fluid

The 4WD systems in pickups and SUVs have an additional gearbox-a torque transfer coupling or a transfer case. If this mechanism is not part of the final drive (as in some carlike SUVs), drain the fluid separately. The factory-recommended fluid may be gear oil or ATF, depending on design requirements. Change the lube when you change transmission fluid.

Coolant

It shouldn't be, but in the real world, a complete coolant replacement is rare. Most people just drain the radiator, which holds 25% to 40% of the total coolant supply. That's why extended-life coolants have such appeal to vehicle makers. However, even these fluids typically carry a drain-and-fill limit of five years, no matter what the mileage, compared with 2 years/30,000 miles for conventional American antifreeze. What's more, their long-life characteristics are based on maintaining a full system and a 50% to 60% antifreeze concentration for the full period, without topping up with water.

There are many different formulas for extended-life coolants, and the color of the dye is meaningless, just as it is with conventional coolants. If you use a drain-and-fill machine or take the time to manually drain the radiator, engine and heater core, you can switch brands without worry if you choose, and follow the service intervals of the coolant producer. Note: A number of extended-life antifreezes were formulated for aluminum radiators and heaters, and do not provide equivalent protection against lead-solder joint corrosion in copper-brass radiators. If the original aluminum radiator has been replaced with a conventional copper-brass design, use a conventional American coolant, even if its service interval is shorter.